This application claims priority to an application entitled xe2x80x9cEcho Canceling Device and Methodxe2x80x9d filed in the Korean Industrial Property Office on Nov. 4, 1998 and assigned Ser. No. 98-47094, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to echo canceling, and in particular, to a device and method for preventing the degradation of echo canceling performance due to saturation.
2. Description of the Related Art
In general, a term xe2x80x9cechoxe2x80x9d refers to a phenomenon when the sound output from a speaker is fed back to a microphone and then is output again through the speaker or returns through a wire or wireless line. When this feedback occurs, it is difficult to restore the original sound. In most cases, the feedback is so great that it drowns out the original signal by generating a high-pitched tone.
Referring to FIG. 1, there is shown a block diagram of a prior art device for echo canceling. First and second amplifiers 100 and 1amplify analog input signals, while analog-to-digital (A/D) converters 100 and 160 convert analog input signals to digital signals. In addition, digital-to-analog (D/A) converters 130 and 150 convert digital input signals to analog signals, while a digital signal processor (DSP) 140 performs echo canceling according to an echo canceling routine prepared therein in addition to general audio processing. An third amplifier 170 amplifies an input signal and provides the amplified signal to an input/output (I/O) connector 190, and an fourth amplifier 180 amplifies a signal input from the input/output connector 190. Finally, input/output connector 190 is connected to other internal or external audio processing blocks.
In an attempt to solve the echo problem of the prior art, the digital signal processor 140 performs convolutional coding for an audio signal input through a microphone and subtracts a specific value obtained by the coding from an audio signal output from a speaker. In this manner, the feedback is suppressed.
More specifically, an audio signal input through the microphone is input to the amplifier 100 designed to have a constant gain. The signal amplified by the amplifier 100 is then converted to a digital signal by the analog-to-digital converter 120. The converted digital audio signal undergoes convolutional coding with a specific filtering coefficient in the digital signal processor 140. A value obtained by convolutional coding is subtracted from a signal output to the speaker, thereby suppressing the echoes. However, in this echo canceling method, when the surrounding sounds of the external environment increase in level, the filtering coefficient and the input sounds exceed (or saturate) the processing limit of the digital signal processor. This results in the degradation of echo canceling performance.
It is, therefore, an object of the present invention to provide a device and method for preventing the degradation of echo canceling performance due to saturation.
To achieve the above object, the present invention provides an echo canceling device comprising a first variable amplifier for variably amplifying an audio signal input through a microphone. The first variable amplifier responds to a control signal generated by a digital signal processor. The echo canceling device also comprises a first analog-to-digital converter for converting an analog signal output from the first variable amplifier to a digital signal. In addition, a second digital-to-analog converter is included for converting a digital signal output from the digital signal processor to an analog signal. There is similarly provided a second variable amplifier for variably amplifying a signal output from the second digital-to-analog converter, an input/output connector for connecting a signal output from the second variable amplifier to internal and external processing devices, and a sound measurer for measuring a level of surrounding sounds input through the microphone. The digital signal processor executes an echo canceling routine, performs general digital signal processing, and generates the control signals for controlling the first and second variable amplifiers according to the sound level measured by the sound measurer.